Robotic surgical systems such as those used in performing minimally invasive surgical procedures offer many benefits over traditional open surgery techniques, including less pain, shorter hospital stays, quicker return to normal activities, minimal scarring, reduced recovery time, and less injury to tissue. Consequently, demand for minimally invasive surgery using robotic surgical systems is strong and growing.
To perform a minimally invasive surgical procedure on a patient, one or more incisions are first made in the patient and cannulae inserted therein to gain access to a surgical site within the patient. Setup arms supporting the slave manipulators (or robotic arm assemblies) are then positioned so as to allow the slave manipulators to attach to respective of the cannulae. Surgical instruments engaged on the slave manipulators are then inserted into the cannulae and properly positioned and oriented in order to perform the procedure. A surgeon may then manipulate master manipulators (or master input devices) which are coupled to the slave manipulators and their respective surgical instruments through one or more controllers to perform the surgical procedure.
The initial positioning and orientating of the surgical instrument at the surgical site is generally performed by an assistant, positioned next to the patient, manually moving a slave manipulator so as to move its surgical instrument into the proper position and orientation to and at the surgical site. Typically such positioning and orientating involves a two-step procedure in which, in a first part, the slave manipulator is attached to its assigned cannula and its surgical instrument engaged on it, and in a second part, the slave manipulator is manipulated so that its surgical instrument is properly positioned and oriented at the surgical site to perform its role in the minimally invasive surgical procedure. Although described as a two-part procedure, it is to be appreciated that the assistant may perform both parts concurrently or otherwise in an overlapping fashion, as well as sequentially so as to be performed one after the other.
To perform the first part of the initial positioning of a surgical instrument, the assistant depresses a first release button on a slave manipulator, which releases brakes holding setup joints of its corresponding setup arm in place so as to allow movement of the slave manipulator. The positioning of the slave manipulator is conventionally facilitated by the use of gravity-balanced or non-gravity loaded setup joints. After the slave manipulator is positioned so that it can be attached to its assigned cannula and is attached to it, the assistant may then stop depressing the first release button, which causes the brakes to hold their corresponding setup joints in place, thus locking the translational position of the cannula attached to the slave manipulator at this point. Additional details in performing this part of the procedure and the general construction of slave manipulators and their setup arms as pertaining to such procedure are provided in commonly owned U.S. Pat. No. 6,246,200 entitled “Manipulator Positioning Linkage for Robotic Surgery,” which is incorporated herein by this reference.
To perform the second part of the initial positioning of the surgical instrument, the assistant engages the surgical instrument onto the slave manipulator so that it is capable of inserting it into the cannula, pivoting the instrument around a pivot point located at the surgical port of the cannula, and driving an end effector at the distal end of the surgical instrument with degrees of freedom resembling wrist motion. It may be noted at this point that the surgical instrument tip is inside the cannula and thus, is no longer visible to the assistant since it is now shielded by the anatomy.
To proceed, the assistant depresses a second button on or proximate to its slave manipulator, which disengages active joints of the slave manipulator from being controlled by their associated master manipulator. This allows the assistant to freely move the slave manipulator to insert the surgical instrument into its cannula and pivot about it about the incision so as to point in the proper direction and at the proper distance into the incision. If an endoscope has been previously positioned in the patient to view the surgical site, typically this step is performed while the assistant views the image of the surgical site provided by the endoscope. After the surgical instrument is thus positioned at the surgical site, the assistant may then stop depressing the second button, which allows the surgeon to re-engage control of the active joints of the slave manipulator through the master manipulator so that the surgeon may perform the surgical procedure by manipulating the master manipulator. To facilitate the positioning tasks described above, the first and second buttons may be effective only while they are depressed (and thus work as momentary buttons) or they can remain effective after they are released until they are depressed again (and thus work as toggle buttons).
Since the first part of the positioning procedure is performed by moving the gravity-balanced setup joints or non-gravity loaded setup joints outside of the patient's body, internally generated frictional and inertial resistance against manual movement of the slave manipulator is not generally objectionable to the assistant. In the second part of the positioning procedure, however, internally generated frictional and inertial resistance against manual movement of the slave manipulator may be objectionable to the assistant, because a finer control of the instrument tip is required while it is moved inside the surgical cavity. To facilitate easy movement of the slave manipulator during the second part of the positioning procedure, the arm may be mechanically gravity balanced using, for example, counter balance weights, so as to significantly reduce gravity effects and consequently, the force necessary for a person to physically move the slave manipulator. Additionally, the slave manipulator may be designed so as to have very high mechanical efficiency so that the friction does not change much with the force applied to the manipulator, have low friction forces or torque to overcome when moving the manipulator, and have low mass or inertia so that the manipulator may be accelerated with low force or torque.
Although a slave manipulator that does not have all of these mechanical characteristics may not be easy to manually position quickly and accurately, it may be advantageous to give away some of these mechanical characteristics in exchange for other benefits such as larger workspace, smaller footprint, or lighter slave manipulator. In such a design, a control system that is capable of recovering the lighter feeling of the mechanically gravity balanced design is desirable.